The invention relates to liquid level indicators using parameters measurements of sound waves passing along the waveguide and reflected from the surface of the liquid.
As a rule, measuring devices with a waveguide contain reflectors arranged on the waveguide. A sound wave of an impulse acoustic signal propagates along a part of the waveguide which is situated aloft being reflected from the reflectors arranged at known distances and reflects as well from the surface of the liquid. The distance is determined by measuring the propagation time of echo signals. The signals from reflectors serve for calibration and improvement of measurement accuracy.
The USSR author's certificate No. 560144 with the priority to Jan. 21, 1975, Int. Cl. G01F23/28, “Liquid Level Detector” is known that contains an acoustic channel made in the form of a hollow tube with a hole immersed into liquid at the end of which a receiving and emitting device is installed outside the liquid. The internal surface of the acoustic channel is provided with the grooves that form shelves directed towards the receiving and emitting device.
The invention according to the U.S. Pat. No. 4,909,080 with the priority to Aug. 29, 1988, “Ultrasound liquid level detector in a tank” contains a transmitter-receiver and a hollow tube waveguide.
The “Level detector with an acoustic waveguide” according to the French application 2596515, Int. Cl. G01F23/28, has a transducer fixed beyond the liquid and emitting an impulse to a long waveguide whose lower part is immersed into the liquid.
The inventions according to the applications of Great Britain 2265005 and 2265219 with the same priority to Mar. 21, 1992, Int. Cl. G01F23/28, “Liquid Level Detector” are known. A detector contains a tube with a set of reflectors arranged along the length of the tube going upwards from a transducer. Liquid fills the tube to the same level as outside of the tube. There is a layer of sound absorbing mass on the inside surface of the tube. The height of the liquid surface according to the second invention is calculated with regard to the difference between propagation times of the impulses reflected by the two highest and located in liquid reflectors and the difference between propagation times of impulses reflected from the liquid surface and the highest reflector.
The U.S. Pat. No. 5,471,872 with the priority to Jan. 7, 1994, Int. Cl. G01F23/296, “Acoustic Liquid Level Indicator” contains the first acoustic waveguide to which in the process of work acoustic transmitter and receiver are connected and the second acoustic waveguide containing reference reflectors in the form of the holes. The waveguides are connected by a corner section where reflectors meant for angular reflection are installed.
The invention according to the European application EP 845663 with the priority to Nov. 21, 1997, Int. Cl. G01F23/296, “Method of liquid level measurement with the help of ultrasound echo signal” is known. A transducer is installed at the bottom of the reservoir with liquid and a tube with a bench mark is installed on the transducer. The liquid level measurement is performed with the help of a bench mark installed at the distance known beforehand.
The design according to the PCT application 9102950, Int. Cl. G01F23/28, “Method and Device for Liquid Level Detection in Reservoirs Using Acoustic Waveguide” contains the main channel of measurements and the reference one for sound speed measurement in the medium volume. Each channel contains a transmitter-receiver and a waveguide in the form of the tube extending from the bottom of the reservoir to the surface of the medium.
In the considered constructions the problem of acoustic matching of acoustical-electrical transducers of a membrane type having large internal resistance and operating aloft with waveguides is not solved which does not allow to raise radiating power and to increase measurement range.
The closest in the technical essence is the invention described in the application of France 2672678, Int. Cl. G01F23/28, “Method and device for the interface level measurement of two different liquids or liquid and gas”. The device contains several reflectors arranged on a waveguide at different distances from an acoustical-electrical transducer.
The problem of good matching of the membrane acoustical-electrical transducer with the waveguide when working aloft is not solved in this construction as well.